Tar-depleted liquid smoke treatment of food casings

ABSTRACT

A tar-containing aqueous liquid wood smoke is at least partially neutralized under controlled temperature to form a tar-enriched fraction and a tar-depleted liquid smoke fraction, and the latter is used for food casing treatment to facilitate smoke coloring and flavoring of encased foodstuff during processing.

This is a continuation-in-part of copending U.S. application Ser. No.311,909, filed Oct. 16, 1981 in the name of M. D. Nicholson, nowabandoned.

RELATED APPLICATIONS

U.S. application Ser. No. 417,171 entitled "Tar-Depleted Liquid Smoke,"is filed contemporaneously with this application in the name of HermanShin-Gee Chiu, U.S. Application Ser. No. 417,173 entitled "Tar-DepletedLiquid Smoke Treatment of Food Casings" is also filed contemporaneouslywith this application in the name of Myron Donald Nicholson, and U.S.application Ser. No. 261,457 entitled "Liquid Coating Method andApparatus" was filed May 7, 1981 in the names of Chiu et al, now U.S.Pat. No. 4,356,218, issued Oct. 26, 1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to: (a) a method for preparing tar-depletedliquid smoke composition from a tar-containing aqueous liquid smodesolution, (b) a tar-depleted smoke colored and smoke flavored tubularfood casing, (c) a tar-depleted aqueous liquid smoke solution with smokecolor, odor and flavor capability, and (d) a method for preparing asmoke colored and smoke flavored encased food product.

2. Description of the Prior Art

Tubular cellulosic food casings are used extensively for processing agreat variety of meat products and other food items. The food casingsare generally thin-walled tubing of various diameters prepared fromreconstituted materials, such as regenerated cellulose. Cellulosic foodcasings may also be prepared with fibrous webs embedded in the wallthereof, such casings commonly being referred to as "fibrous foodcasings".

The many different recipes and modes of processing that are used by theprocessed food industry to suit different tastes, and even regionalpreferences, generally necessitate the use of food casings with avariety of characteristics. In some instances, for example, food casingsare required to have multifunctional uses wherein they serve ascontainers during the processing of a food product encased therein, andthen also serve as a protective wrapping for the finished product. Inthe processed meat industry, however, the food casings used in thepreparation of many types of meat products, such as various types ofsausages, such as frankfurters, bolognas and the like, beef rolls, hamsand the like, are frequently removed from about the processed meatproduct prior to slicing and/or final packaging.

Surface appearance and flavor are important factors in the commercialand consumer acceptance of processed meat products, and a common featureof most varieties of such products involves the use of "smoking" forimparting characteristic flavor and color thereto. The "smoking" of foodproducts is generally accomplished by the food processor subjecting thefood product to actual contact with smoke in a gaseous or cloud-likeform. Such "smoking" processes, however, have not been consideredcompletely satisfactory for a variety of reasons, including theinefficiencies and lack of uniformity of the "smoking" operation.Because of the shortcomings experienced, many meat packers now employvarious types of liquid aqueous solutions of wood-derived smokeconstituents, commonly called "liquid smoke solutions" that have beendeveloped and used commercially by the food processor in the processingof many types of meat and other food products. For convenience, in thisspecification, the as-purchased "liquid smoke solutions" will befrequently referred to as "as-is" liquid smoke.

The application of "liquid smoke solutions" to meat products isgenerally carried out in a variety of ways, including spraying ordipping an encased food product during the processing thereof, or byincorporating the "liquid smoke solution" in the recipe itself. Theactual operation of "smoking" by spraying or dipping is not completelysatisfactory due to inability to treat the encased product uniformly,and incorporation of "liquid smoke solutions"in the meat recipe does notalways provide the desired surface appearance because of dilution ofsmoke ingredients. Incorporation in the recipe also reduces thestability of the meat emulsion, and will adversely affect taste if highconcentrations are used. Application of liquid smoke to encased foodproducts by the food processor such as by spraying or dipping, alsocauses unwanted pollution and equipment corrosion problems for the foodprocessor. In addition, encased sausages treated by application of theliquid smoke during commercial processing have been found to yield,after peeling the casing from the treated encased food product, sausageswhich are lacking in smoke color uniformity from sausage to sausage, andfrom batch of sausages to batch of sausages. What is even moreundesirable, is the lack of uniformity of coloration which often appearson the surface of the same sausage, including light and dark streaks,light and dark blotches, and even uncolored spots which especiallyappear at the ends of sausages.

It has also been suggested, as for example disclosed in U.S. Pat. No.3,330,669 to Hollenbeck, that application of a viscous liquid smokesolution to the inside surface of a deshirred tubular food casing by thefood processor immediately prior to stuffing the casing with a sausageemulsion, results in preparation of processed food products that exhibitacceptable color and smoky flavor after cooking and removal of thecasing. However, the Hollenbeck procedure has not been found practicaland is not used commercially. The viscous liquid smoke solutiondisclosed by Hollenbeck is not practical for coating a casing on a highspeed production line to produce a coated casing which can then beshirred by conventional methods and used as a shirred casing on anautomatic stuffing machine. The high viscosity of the Hollenbeck coatingsolution limits the casing coating speed and, if a conventional methodsuch as "slugging", also called "bubble coating", is used to coat theinside of the casing, the viscous Hollenbeck coating necessitatesfrequently cutting the casing open to replenish the slug of coatingmaterial within the casing, which results in short lengths of casing andthus makes continuous shirring impractical.

Heretofore, however, it has been found that providing casings whichafford special treatment or structural characteristics to the foodproduct can be more uniformly and economically accomplished by thecasing manufacturer. This is especially true with the advent of, andwide commercial use of, automatic stuffing and processing equipment inthe processed food industry.

Several methods of providing food casings with coatings applied to asurface thereof are known and described in the patent literature. Thereis disclosed, for example, in U.S. Pat. No. 3,451,827 a spraying methodfor applying a variety of coating materials over the internal surface ofsmall diameter casings. In U.S. Pat. No. 3,378,379 to Shiner et al., a"slugging" method is used for applying coating materials to the internalsurface of large diameter casings. While such techniques and others havebeen used in preparing commercial quantities of a variety of coated foodcasings, including casings where liquid smoke is employed as a componentin the coating composition, the casings produced thereby have beendesigned to meet particular commercial requirements and, to the best ofmy knowledge, none of the prior art coated casings disclosed have beenknown to successfully impart a satisfactory level of "smoke" flavor andcolor to a meat product processed therein. For example, in U.S. Pat. No.3,360,383 to Rose et al., and in U.S. Pat. Nos. 3,383,223 and 3,617,312to Rose, there are disclosed coating compositions of various proteinmaterials, such as gelatin, that employ liquid smoke solutions inamounts specifically required to insolubilize the protein materials.Such coated casings are disclosed as exhibiting special adhesionproperties required for the processing of dry sausages, which propertieswould therefore limit the suitability thereof for many other casingapplications.

The prior art patents teach the application of liquid smoke to theinternal surface of a casing, but attempts by the instant inventor tointernally coat casing during the manufacture thereof have been found tobe costly and to limit the speed of a continuous high speed productionline.

One solution of this problem as described and claimed in copendingUnited States application Ser. No. 062,358 filed July 3, 1979 in thename of Herman Shin-Gee Chiu, involves treating the external surface ofthe food casing with an aqueous liquid smoke composition derived fromnatural wood. Chiu also discovered that when the food casing iscellulosic and formed of either non-fibrous gel stock or fibrous gelstock, the use of as-is highly acidic (pH of 2.0 to 2.5) aqueous liquidsmoke results in the formation of a tarry deposit accumulating on thecarrier rolls and the squeeze rolls of the smoke treatment unit, therebyeventually forcing shut-down of the treating system. It was discoveredthat this problem could be overcome by at least partially neutralizingthe as-is liquid smoke to precipitate the tar, and then treating thecellulosic gel stock casing with the tar-depleted liquid smoke. Chiudiscovered that contrary to the previous state-of-art belief, thetar-depleted liquid smoke surprisingly still possesses significant smokecoloring and flavoring capability, and this invention is described andclaimed in his previously referenced United States application Ser. No.417,171 "Tar-Depleted Liquid Smoke and Treated Food Casing", filedcontemporaneously with this application.

One problem with the neutralization method of preparing the tar-depletedaqueous liquid smoke composition of the last-mentioned Chiu applicationis that the coloration capability or "staining power" of thewood-derived liquid smoke declines with increasing pH or neutralization.

One object of this invention is to provide a method for preparingtar-depleted liquid smoke from a tar-containing wood-derived liquidsmoke which avoids at least part of the staining power loss normallyexperienced with neutralization.

Another object of this invention is to provide a tar-depleted aqueousliquid smoke solution with high capability for imparting smoke color,odor and flavor to food products.

Still another object of this invention is to provide a tar-depleted,smoke colored and smoke flavored tubular food casing with highcapability for imparting smoke color, odor and flavor to food productsencased therein, by treatment with the aforementioned solution in turnprepared by the aforementioned method.

A further object of this invention is to provide a method for preparinga smoke colored and smoke flavored food product within theaforementioned tar-depleted, smoke colored and smoke flavored tubularfood casing.

Other objects and advantages of the invention will become apparent fromthe ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

In this invention a method is provided for the preparation of an aqueousliquid smoke composition in which a tar-containing aqueous liquid smokesolution, having an absorptive power (hereinafter defined) of at leastabout 0.25 at 340 nm. wave length, is provided at temperature belowabout 40 ° C. This tar-containing aqueous liquid smoke solution is atleast partially neutralized by contacting a high pH constituenttherewith in sufficient quantity to raise the pH of the smoke solutionto a level above about 4, thereby forming a tar-enriched fraction and atar-depleted liquid smoke fraction. The temperature of this solution iscontrolled during the neutralization so that the solution temperaturedoes not rise above about 40° C. The tar-enriched fraction and thetar-depleted liquid smoke fraction are separated to recover the latteras the aqueous liquid smoke composition of the present invention.

The invention also includes a tar-depleted liquid smoke treated tubularfood casing prepared by steps including the provision of atar-containing aqueous liquid smoke solution at temperature below about40° C., said smoke solution having an absorptive power of at least about0.25 at 340 nm. wave length. This tar-containing aqueous liquid smokesolution is at least partially neutralized by contacting a high pHconstituent therewith in sufficient quantity to raise the pH of thesmoke solution to a level above about 4, thereby forming a tar-enrichedfraction and a tar-depleted liquid smoke fraction. The temperature ofthis solution is controlled during the neutralization so that thesolution temperature does not rise above about 40° C. The tar-enrichedfraction and tar-depleted liquid smoke fraction are separated to recoverthe latter as a tar-depleted liquid smoke composition. A surface of atubular food casing is treated with the tar-depleted liquid smokecomposition in sufficient quantity to provide an absorptive index(hereinafter defined) of at least about 0.2 at 340 nm. wave length forthe casing wall.

This invention further includes a tar-depleted liquid smoke compositionwith smoke color, odor and flavor capability, prepared by providing atar-containing aqueous liquid smoke solution at temperature below about40° C., said smoke solution having an absorptive power of at least about0.25 at 340 nm. wave length. This aqueous liquid smoke solution is atleast partially neutralized by contacting a high pH constituenttherewith in sufficient quantity to raise the pH of the smoke solutionto a level above about 4, and thereby form a tar-enriched fraction and atar-depleted liquid smoke fraction. The temperature of the aqueousliquid solution is controlled during the neutralization so that thesolution temperature does not rise above about 40° C. The tar-enrichedfraction and a tar-depleted liquid smoke fraction are separated torecover the latter as the aqueous liquid smoke composition, with theneutralizing and simultaneous temperature controlling steps, and theseparating step being performed so as to provide an aqueous liquid smokecomposition with at least 50% light transmittance as determined by ananalytical method which is disclosed hereinafter.

Still another aspect of this invention relates to a method for producinga smoke colored and smoke flavored foodstuff product including the stepsof providing a tar-containing aqueous liquid smoke solution comprising amixture of smoke color, odor and flavor constituents having anabsorptive power of at least about 0.25 at 340 nm. wave length. Theaqueous liquid smoke solution is at least partially neutralized bycontacting a high pH constituent therewith in sufficient quantity toraise the pH of the smoke solution to a level above about 4 and therebyform a tar-enriched fraction and a tar-depleted liquid smoke fraction.The temperature of the aqueous liquid smoke solution is controlledduring the neutralization so that the temperature does not rise aboveabout 40° C. The tar-enriched fraction and tar-depleted liquid smokefraction are separated and the latter is recovered as a tar-depletedliquid smoke composition. A surface of a tubular food casing is treatedwith the tar-depleted liquid smoke composition in sufficient quantity toprovide an absorptive index of at least about 0.2 at 340 nm. wave lengthfor the casing wall. The so-treated casing is stuffed with foodstuff,and the resulting encased foodstuff is processed so as to impart smokecolor, odor and flavor to the encased foodstuff by transfer to smokecolor and smoke flavor constituents from the casing to the encasedfoodstuff.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of apparatus suitable for treatment of foodcasing external surface with tar-depleted liquid smoke in accordancewith one embodiment of this invention.

FIG. 2 is a schematic view of apparatus similar to and performing thesame function as the FIG. 1 apparatus, but with a chamber for partiallydrying the tar-depleted liquid smoke treated casing to a desiredmoisture content while in an inflated condition.

FIG. 3 is a schematic view of apparatus similar to and preforming thesame function as the FIG. 2 apparatus but with means for partiallydrying the tar-depleted liquid smoke treated casing while in a flatcondition.

FIG. 4 is a graph showing tar-depleted liquid smoke staining power as afunction of partial neutralization temperature.

FIG. 5 is a graph showing tar-depleted liquid smoke light transmittanceas a function of the composition pH.

FIG. 6 is a graph showing ultraviolet transmittance and ultravioletabsorbance at various wave lengths for both as-is tar-containing liquidsmoke and tar-depleted liquid smoke of this invention.

FIG. 7 is a graph showing ultraviolet absorptive index as a function oftar-depleted liquid smoke loading on a food casing external surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Food casings that are suitable for use in the present invention aretubular casings, and preferably tubular cellulosic casings, that areprepared by any one of the methods well known in the art. Such casingsare generally flexible, thin-walled seamless tubing formed ofregenerated cellulose, cellulose ethers such as hydroxyethyl cellulose,and the like, in a variety of diameters. Also suitable are tubularcellulosic casings having a fibrous reinforcing web embedded in the wallthereof, which are commonly called "fibrous food casings", as well ascellulosic casings without fibrous reinforcement, herein referred to as"non-fibrous" cellulosic casings.

Casings conventionally known as "dry stock casings" may be used in thepractice of this invention. Such casings generally have a water contentwithin the range of from about 5 to about 14 weight percent water ifnon-fibrous casing, or within the range of from about 3 to about 8weight percent water if fibrous casing, based on the total weight ofcasing including water.

Casings conventionally known as "gel stock casings" are casings whichhave higher moisture contents since they have not been previously dried,and such casings may also be used in the practice of this invention. Gelstock casings, whether fibrous or non-fibrous, are the type exhibitingthe aforementioned tarring problem when treated by as-is liquid smoke.

Smoke color, odor and flavor constituents suitable for use in accordancewith the present invention are generally those designated as being thecolor, odor and flavor constituents of as-is liquid smoke.

The term "solution" as used herein is meant to encompass homogeneoustrue solutions, emulsions, colloidal suspensions and the like.

Liquid smoke often is a solution of natural wood smoke constituentsprepared by burning a wood, for example, hickory or maple, and capturingthe natural smoke constituents in a liquid medium such as water.Alternatively, the liquid smoke to be used may be derived from thedestructive distillation of a wood, that is, the breakdown or crackingof the wood fibers into various compounds which are distilled out of thewood char residue. Aqueous liquid smokes are generally very acidic,usually having a pH of 2.5 or less and a titratable acidity of at least3% by weight.

Reference to the term "smoke color, odor and flavor constituents", asused throughout this specification and in the appended claims withrespect to the liquid smoke compositions and casings of this invention,is intended to refer to, and should be understood as referring to, thesmoke color, odor and flavor constituents derived from liquid smokesolutions in their commercially available form.

The tar-depleted liquid smoke composition of this invention is derivedfrom natural wood smoke constituents. The source liquid smoke isgenerally produced by the limited burning of hardwoods and theabsorption of the smoke so generated, into an aqueous solution undercontrolled conditions. The limited burning keeps some of the undesirablehydrocarbon compounds or tars in an insoluble form, thereby allowingremoval of these constituents from the final liquid smoke. Thus, by thisprocedure, the wood constituents previously considered desirable by themanufacturers are absorbed into the solution in a balanced proportionand the undesirable constituents may be removed. The resultant liquidsmoke solution still contains a significant concentration of tarsbecause the manufacturers and users consider the dark colored tars to benecessary from the standpoint of imparting smoke color and smoke flavorto foodstuffs. This smoke solution is representative of the wholespectrum of wood-derived smoke colors, odors and flavors that areavailable. The apparatus and method for manufacturing typical liquidsmokes of the preferred type is more fully described in U.S. Pat. Nos.3,106,473 to Hollenbeck and 3,873,741 to Melcer et al.

As used herein, the term "at least partially neutralized" is intended torefer to liquid smoke compositions having a pH greater than about 4,preferably having a pH within the range of from about 5 to about 9, andmore preferably having a pH within the range of from about 5 to about 6.

The tar-depleted liquid smoke composition may be applied to the externalsurface of the tubular casing by passing the casing through a bath ofthe tar-depleted liquid smoke composition. The liquid smoke is allowedto contact the casing prior to doctoring off any excess liquid smoke bypassing the casing through squeeze rolls, or wipers, and the like, foran amount of time sufficient for the casing to incorporate the desiredamount of smoke coloring and flavoring constituents. The process ofpassing the casing through a treatment bath, also referred to in the artas a "dip bath" or a "dip tank," may also be referred to in the art as a"dipping" step. The liquid smoke composition may alternatively beexternally applied to the casing by methods other than dipping, such asspraying, brushing, roll-coating, and the like.

Alternatively, the tar-depleted liquid smoke composition may be appliedto the internal surface of the casing by any of several well-knownprocedures described in U.S. Pat. No. 4,171,381 to Chiu, the disclosureof which is incorporated by reference. These include slugging or bubblecoating, spraying, and coating while shirring. The slugging method forcoating the inside of a casing involves filling a portion of the casingwith the coating material, so that the slug of coating materialgenerally resides at the bottom of a "U" shape formed by the casingbeing draped over two parallel rollers, and then moving the continuousindefinite length of casing so that the slug of coating material remainsconfined within the casing, while the casing moves past the slug and iscoated on its inside wall by the coating material contained within theslug.

It may then be shirred by conventional methods, or prior to shirring, itmay be dried and/or humidified to a water content suitable for shirringand/or further processing. The need for conventional drying and/orhumidification after the preferably external tar-depleted liquid smoketreatment depends on the water content of the casing after treatment andthe type of casing. If the casing is a non-fibrous casing, a watercontent within the range of from about 8 weight percent to about 18weight percent water immediately before shirring is typical, and forfibrous csing a water content within the range of from about 11 weightpercent to 35 weight percent water immediately before shirring istypical, where percent is based on the total weight of casing includingwater.

One method of treating the casing with the tar-depleted liquid smoke ofthis invention is shown in FIG. 1. In FIG. 1, a flattened, tubular,cellulosic sausage casing 10, is externally treated with a tar-depletedliquid smoke composition during its passage over lower and upper guiderolls 13 through dip tank 11 which contains the tar-depleted liquidsmoke composition 12. The casing passes over lower and upper guide rolls14 after exiting the dip tank, and then passes between squeeze rolls 20which minimize any excess carry-over of the liquid smoke composition.The total contact time of the casing 10 with the tar-depleted liquidsmoke composition 12 in the dip tank 11, and with excess liquid smokecomposition on the casing passing over the guide rolls 14 before thecasing passes through the squeeze rolls 20, will determine the amount ofsmoke coloring and flavoring constituents of the tar-depleted liquidsmoke composition that the casing will incorporate. The total contacttime is measured from point A to point B in FIG. 1. After the casingpasses through squeeze rolls 20, it passes over guide roll 23 and iswound up on reel 24. The casing is then sent on to conventional furtherprocessing, including conventional humidification, as may be required,and conventional shirring.

The embodiment illustrated in FIG. 2 differs from that illustrated inFIG. 1, in that in FIG. 2 the casing after passing through squeeze rolls20 is passed into a heating and drying chamber 21, wherein it is driedto the proper moisture content. The casing is inflated by a bubble ofair maintained in a relatively fixed position betwen squeeze rolls 20and 22 by the sealing action of rolls 20 and 22. The heating chamber 21can be any type of heating device, such as circulating hot air chambers,which will dry the sausage casing to the proper moisture content. Afterthe casing passes out of the heating chamber 21 and through squeezerolls 22, it passes over guide roll 23 and is wound up on reel 24. Thecasing is then sent on to conventional further processing, includingconventional humidification, as may be required, and conventionalshirring.

The embodiment illustrated in FIG. 3 differs from that illustrated inFIG. 2, in that in FIG. 3 the casing is dried in a flat condition whilepassing over guide rolls 25.

It is to be noted that the tar-depleted liquid smoke which is coated onthe casing surface, whether externally coated or internally coated, doesnot exist solely as a surface coating. Smoke color, odor and flavorconstituents which are coated on the surface penetrate the cellulosicstructure of the casing as the cellulose absorbs the moisture of thesmoke solution. Inspection of the cross-section of the casing walldiscloses a color gradation across the casing wall, with the smoketreated surface having a darker color than the surface on the oppositeside of the casing wall. Accordingly, as used herein, the term "coating"is to be understood to mean that the casing wall is not only coated withsmoke constituents but that the casing wall is also impregnated withsmoke constituents.

The tar-depleted liquid smoke compositions of the present invention mayalso contain other ingredients which may be suitably used in treating atubular food casing, to which the smoke constituents are applied, e.g.,glycerine and/or propylene glycol which may be used as humectants orsoftening agents, and the like.

Other ingredients which are normally used in the manufacure of, orfurther treatment of the food casings, e.g., cellulose ethers andmineral oil, may also be present in the casing if desired, and they maybe used in the same manner and amounts as if the tar-depleted liquidsmoke treatment had not been used.

In particular, agents for improving the peelability of the casings fromfood products such as sausages, e.g., frankfurters, bolognas and thelike, may be optionally coated on the internal surface of the casingsbefore or after the external application of tar-depleted liquid smoke tothe casing, and before or during shirring. If The tar-depleted liquidsmoke is applied to the casing internal surface, the peelability agentis preferably applied first. Such peelability enhancing agents include,but are not limited to, carboxymethyl cellulose and other water solublecellulose ethers, the use of which is disclosed in U.S. Pat. No.3,898,348 issued Aug. 5, 1975 to Chiu et al., the disclosure of which isincorporated herein by reference; "Aquapel" a Hercules, Inc. trademarkedproduct comprising alkyl ketene dimers, the use of which is furtherdisclosed in U.S. Pat. No. 3,905,397 issued Sept. 16, 1975 to H. S.Chiu, the disclosure of which is incorporated herein by reference; and"Quilon", an E. I. duPont de Nemours Co., Inc. trademarked product whichis a fatty acid chromyl chloride, the use of which is further disclosedin U.S. Pat. No. 2,901,358 issued Aug. 25, 1959 to Underwood et al., thedisclosure of which is incorporated herein by reference.

If a fibrous casing is externally treated with an at least partiallyneutralized tar-depleted liquid smoke, carboxymethyl cellulose or otherwater soluble cellulose ethers are coated after liquid smoke treatment,but "Aquapel" or "Quilon" may be coated on the internal surface of thecasing to improve peeling properties, either before or aftertar-depleted liquid smoke treatment. If a non-fibrous casing isexternally treated with an at least partially neutralized tar-depletedliquid smoke then, carboxymethyl cellulose or other water solublecellulose ethers are the preferred materials to be coated on theinternal surface of the casing to improve peeling properties.

The peelability enhancing agent may be applied to the internal surfaceof the tubular food casings by using any one of a number of well knownmethods. Thus, for example, the peelability enhancing agent can beintroduced into the tubular casing in the form of a "slug" of liquid, ina manner similar to that disclosed, for example, in U.S. Pat. No.3,378,379 to Shiner et al. Advancing the casing past the liquid slugcoats the inner surface thereof. Alternatively, the peelabilityenhancing agent may be applied to the internal surface of the casingthrough a hollow mandrel over which the casing is advancing as, forexample, a shirring machine mandrel in a manner similar to thatdescribed in U.S. Pat. No. 3,451,827 to Bridgeford.

Casings may be prepared according to this invention, which are suitablefor the processing of what is conventionally known in the art as "drysausages." Unlike other types of non-fibrous and fibrous casings whichare preferably easy to peel from the food product, either by the foodprocessor before sale to the customer or by the consumer, "dry sausage"casing preferably adheres to the food product during and afterprocessing. "Kymene," a Hercules, Inc. trademarked product which is apolyamide epichlorohydrin resin, the use of which is further disclosedin U.S. Pat. No. 3,378,379 issued Apr. 16, 1968 Shiner et al., thedisclosure of which is incorporated herein by reference, may beinternally coated on the internal surface of a casing treated withtar-depleted liquid smoke by the method of this invention, to improvethe adhesion of the casing to food products processed therein.

The at least partial neutralization step of this invention may beaccomplished by mixing either a highly alkaline solid with thetar-containing liquid smoke, as for example CaCO₃, NaHCO₃, Na₂ CO₃soda-lime mixture, and NaOH pellets or flake, or by mixing a high pHliquid such as aqueous NaOH solution. However, the carbonate andbicarbonate solids produce violent foaming, which may cause operationaldifficulties, and they, therefore, are not preferred. Although anaqueous base such as 50% NaOH may be used, tests have shown that atleast partial neutralization with solid NaOH yields a liquid smoke whichretains a higher percentage of the initial staining power of the as-istar-containing liquid smoke. The lower staining power observed withaqueous NaOH neutralization is due in part to the dilution incurred whenusing 50% caustic. By way of illustration, approximately 90-95% of theinitial staining power of Royal Smoke AA liquid smoke (purchased fromGriffith Laboratories, Inc.) can be retained when neutralizing withsolid NaOH, as compared with the retention of 80-85% of the initialstaining power when neutralizing with aqueous 50% NaOH. Since NaOHpellets are more difficult to dissolve than flake, NaOH flake is thepreferred physical form of the neutralizing agent.

By way of illustration, based on a 110 gallon batch of Royal Smoke AAas-purchased (as-is) liquid smoke having a pH of 2.5, thirty four pounds(15.4 kg) of water is produced when solid NaOH is the partialneutralization agent and the desired pH is 6.0. In comparison, 109pounds (49.4 kg) of water results when aqueous 50% NaOH is used, whichis about a 200% increase. Assuming the as-is tar-containing liquid smokeis 70% by weight water, solid NaOH yields a partially neutralizedtar-containing liquid smoke of 68% water, versus 70% water when usingaqueous 50% NaOH for partial neutralization.

The rate of base material addition to the tar-containing liquid smokedepends on the cooling capacity of the mixing container as well as theefficiency of the mixing means, as will be understood by those skilledin the art. As will be demonstrated by ensuing examples, the stainingpower of the at least partially neutralized and tar-depleted liquidsmoke is not substantially affected by temperature variations during theat least partial neutralization step, as long as the temperature of thebulk liquid is maintained below about 30° C.

The mixing container should be cooled by indirect means, as for example,brine circulating through immersed coils in a closed-circuitrefrigeration system. The reason for indirect rather than direct contactbetween the refrigerant and the liquid smoke is to avoid contaminationof the latter.

By way of illustration, and based on a 125 gallon (473 liter) capacitycylindrical container of 31 inches (78.7 cm) diameter and 42 inches (107cm) height, with a "Lightnin" submerged propeller-type mechanical mixer(manufactured by Mixing Equipment Company, Rochester, NY), and withbrine-containing immersed cooling coils as part of a refrigerationsystem having a cooling capacity of 5 tons (17,600 joules/sec), theaddition of fifteen pounds (6.80 kg) of NaOH flakes per hour for fivehours is suitable for partially neutralizing a 110 gallon 416 literbatch of Royal Smoke AA from a pH of 2.5 to a pH of 6.0 whilemaintaining the temperature below 30° C.

Another possible method for at least partially neutralizing thetar-containing liquid smoke is by contacting the latter with anion-exchange material.

The invention will be more clearly understood by reference to thefollowing examples which are set forth as being merely illustrative ofthe invention and which are not intended, in any manner, to belimitative thereof. Unless otherwise indicated, all parts andpercentages are by weight and all casing related percentages are basedon the total weight of the casing. Commercially available as-is liquidsmokes useful in the practice of this invention include certain gradesof both "Charsol" purchased from Red Arrow Products Co. and "RoyalSmoke" purchased from Griffith Laboratories, Inc.

EXAMPLE I

This example illustrates the preparation of a tar-depleted liquid smokecomposition of this invention. To (980 lb, 417 liter, 445 kg) of RoyalSmoke AA as-is liquid smoke solution, at a pH of 2.5 and having anabsorptive power of about 0.65 at 340 nm. wave length, 73 lbs. 33.1 kgof flake NaOH was added at the rate of 2 lbs/minute (0.91 kg/min). Thevessel was stirred continuously and cooled with a chilled brine jacket.The temperature varied in the range of 14°-17° C. during the processing.Upon completion of the partial neutralization to a pH of 6.0, thestirring was stopped and the tars were allowed to settle overnight. Thetap precipitate and the tar-depleted supernatant liquid were gravityseparated and the latter was subsequently filtered through a sub-micronfilter cartridge. The resulting aqueous liquid smoke composition wassubstantailly tar-free as determined by a qualitative watercompatibility test in which liquid smoke was mixed with water andobserved for tar precipitation or lack thereof. There was no visableprecipitation of tar. The chemical compositions of the as-is liquidsmoke and the tar-depleted liquid smoke of this Example are shown inTable A.

                  TABLE A                                                         ______________________________________                                        Chemical Comparison* of Commercially Available                                Liquid Smoke and Tar-Depleted Liquid Smoke                                    Composition of this Invention                                                           Phenols  Carbonyls Total Acid                                                 mg/g     mg/g      Content %                                        ______________________________________                                        As-is liquid                                                                              5.2         71       11.5                                         smoke (pH 2.4)                                                                Tar-Depleted                                                                              3.5        120       14.6                                         liquid smoke                                                                  (pH 6.0)                                                                      ______________________________________                                         *Numbers are arithmetic averages of multiple determinations              

Table A shows that the tar-depleted aqueous liquid smoke compositionprepared in accordance with this invention has a substantially differentchemical character from the as-is tar-containing aqueous liquid smoke.It will be noted that the phenol content is somewhat less, but thecarbonyl and total acid content of the tar-depleted liquid smoke areboth apparently higher than the corresponding values for the originaltar-containing liquid smoke. A possible explanation is that,constituents such as carbonyls and acids, which are highly volatile inthe free state (pH of 2) but not as volatile in their salt form (pH of6), may be lost partially in the analytical procedure where samplepreparation involves distillation and recovery. The procedure fordetermining total acid content is the steam distillation-titrationtechnique described hereinafter. The procedures for determining phenoland carbonyl content in liquid smoke are as follows.

Determination of Phenol and Carbonyl Content of Liquid Smoke

For sample preparation, all samples are filtered through Whatman No. 2filter paper or equivalent, and refrigerated upon receipt or afterpreparation until the time of analysis to avoid possible polymerization.Distilled water is used for all dilutions. The samples are diluted withwater in two steps, beginning with a 10 ml. quantity. In the first stepthe dilution is to a total volume of 200 ml., and in the second step 10ml. of the first solution is further diluted to a total volume of 100ml. For phenol determination, 5 ml. of the second solution is furtherdiluted in a third step with distilled water to a total volume of 100ml. For carbonyl determination, 1 ml. of the second solution is furtherdiluted with carbonyl-free methanol to a total volume of 10 ml.

For the phenol determination the reagents are:

1. Boric acid-potassium chloride buffer pH 8.3. Dilute the indicatedquantities of the solution to 1 liter with water.

0.4 M Boric Acid--125 ml.

0.4 M Potassium chloride--125 ml.

0.2 M Sodium hydroxide--40 ml.

2. 0.6% NaOH

3. Color reagent-N-2,6-trichloro-p-benzoquinoneimine

Stock solution: Dissolve 0.25 gm, in 30 ml. methanol and keep inrefrigerator.

4. 2,6-Dimethoxyphenol standards Prepare solutions of 1 to 7micrograms/ml. of DMP in water for standard curve.

This procedure for phenol determination is a modified Gibbs method basedon the procedure described in Tucker, I. W. "Estimation of Phenols inMeat and Fat", JAOAC, XXV, 779 (1942). The reagants are mixed togetherin the following order:

1st--5 ml. of pH 8.3 buffer.

2nd--5 ml. of dilution of unknown diluted liquid smoke, or of standard2,6-dimethoxyphenol solution, or 5 ml. of water for blank.

3rd--Adjust pH to 9.8 using 1 ml. of 0.6% NaOH.

4th--Dilute 1 ml. of color reagent stock solution to 15 ml. in water.Add 1 ml. of diluted color reagent. Prepare just before adding.

5th--Allow color to develop for exactly 25 minutes at room temperature.

6th--Determine absorbance at a wave length of 580 nm in a 1 cmcolorimeter tube with a Spectronic 20 or equivalent.

7th--Prepare a standard curve using absorbance as the abscissa andstandard concentrations as the ordinate. Extrapolate concentration ofDMP in liquid smoke dilutions from this curve.

8th--Calculate mg DMP/ml liquid smoke using the following equation:##EQU1## To calculate mg DMP/g liquid smoke, divide result of aboveequation by the weight (g) of 1 ml. of liquid smoke.

For carbonyl determination, the reagents are:

1. Carbonyl-free methanol. To 500 ml. of methanol add 5 gm. of2,4-dinitrophenylhydrazine and a few drops of concentrated HCl. Refluxthree hours, then distill.

2. 2,4-Dinitrophenylhydrazine solution. Prepare saturated solution incarbonyl-free methanol using twice recrystallized product. Store inrefrigerator and prepare fresh every two weeks.

3. KOH solution. Add 10 gm. of KOH solid to 20 ml. of distilled H₂ O anddilute to 100 ml. with carbonyl-free methanol.

4. 2-Butanone standard. Prepare solutions of 3.0 to 10 mg. of 2-butanonein 100 ml. carbonyl-free methanol for a standard curve.

The procedure is a modified Lappan-Clark method based on the proceduredescribed in their article "Colorimetric Method for Determination ofTraces of Carbonyl Compounds", Anal. Chem. 23, 541-542 (1959). Theprocedure is as follows:

1st--To 25 ml. volumetric flasks containing 1 ml. of2,4-dinitrophenylhydrazine reagent (prewarmed to insure saturation) add1 ml. of diluted liquid smoke solution, or 1 ml. of standard butanonesolution, or 1 ml. of methanol (for reagent blank).

2nd--Add 0.05 ml. of concentrated HCl to all 25 ml. flasks, mix contentsof each, and place in water bath for 30 minutes at 50° C.

3rd--Cool to room temperature and add 5 ml. KOH solution to each.

4th--Dilute contents of each flask to 25 ml. with carbonyl-freemethanol.

5th--Read at 480 nm against methanol blank set at absorbance of 0,(cuvettes-0.5×4 in (10.2 cm) or equivalent). Use Spectronic 20, orequivalent.

6th--Plot absorbance versus 2-Butanone (MEK) concentration in mg. per100 ml. for standard curve.

7th--Prepare a standard curve using absorbance as the abscissa andstandard concentrations (mg MEK/100 ml.) as the ordinate. Extrapolateconcentration of MEK in liquid smoke dilutions from this curve.

8th--Calculate mg MEK/100 ml. liquid smoke by the following equation:##EQU2## To calculate mg MEK/g liquid smoke, divide the result of theabove equation by the weight (in grams) of 100 ml. of smoke.

EXAMPLE II

This example illustrates the treatment of non-fibrous cellulose casingby the method of this invention with the tar-depleted liquid smoke ofExample I. For comparison, the same type of casing was treated in thesame manner with the as-is tar-containing Royal Smoke AA liquid smoke.

Several non-fibrous frankfurter size gel stock casings were treated withthe aqueous liquid smoke compositions of Example I by applying theliquid smoke solutions to the external surfaces of the casings. Theapplicator was a device which uniformly distributed the aqueous liquidsmoke solution around the casings and comprised two main parts: theliquid smoke applicator and the smoothing unit. The smoke applicatorconsisted of a stationary foam disc mounted such that the liquid smokeentered at the outer edge. Tiny flexible plastic tubes conducted theliquid to the center core where the inflated casing was passed through.The foam disc flexes with casing sizes, thereby making it suitable for arange of casing cross-sectional areas. Because the liquid smokeapplication is not precisely uniform, a rotating smoothing device wasused immediately after the applicator. It contained a rotating foam discwith a core size suitable for the casing size being processed. The discwas driven by an air motor at 200 to 250 rpm. Excess liquid smoke fromthe applicator and from the smoothing device was collected in a commonsump and returned to the applicator inlet. The treated casings weremoved through a point support-type assembly to and through a dryingsection. The aforedescribed coating and casing movement assembly is notpart of the present invention but is claimed in previously referencedcopending application Ser. No. 261,457, entitled "Liquid Coating Methodand Apparatus", filed May 7, 1981 in the names of Chiu et al. andincorporated herein to the extent pertinent.

The treated casings were dried at 80° C. to a water content of 12 weightpercent. The casings were then conventionally moisturized to 14-18weight percent water, and shirred. Each of the treated casings containedabout 10 mg/in² (1.55 mg/cm²) of liquid smoke, and the phenols,carbonyls and total acid content present in the treated casings areshown in Table B. The procedure for measuring total acid content is thesteam distillation technique described hereinafter.

                  TABLE B                                                         ______________________________________                                        Chemical Comparison* of Non-Fibrous                                           Cellulose Casings Treated with Liquid Smoke                                                                    Total Acid                                              Phenols    Carbonyls  Content                                      Casing Sample                                                                            mg/100 cm.sup.2                                                                          mg/100 cm.sup.2                                                                          mg/100 cm.sup.2                              ______________________________________                                        Treated with as-                                                                         0.20       9.6        7.75                                         is liquid smoke                                                               (pH 2.4)                                                                      Treated with tar-                                                                        0.15       6.4        15.8                                         depleted liquid                                                               smoke (pH 6.0)                                                                ______________________________________                                         *Numbers are arithmetic average of multiple determinations               

Because of the nature of these experiments, the phenol reduction in theliquid smoke (Table A) and the phenol reduction in the coated casing(Table B) are not proportionate. As in the case of Table A, noconclusion can be drawn from my work with respect to the effect of thisinvention on carbonyl content or total acid content of the casing.Relative to the total acid content, the higher level in the partiallyneutralized and tar-depleted casing sample reflects the lower volatilityof the salt form of the acids at higher pH. That is, the sodium acetateis not volatilized in the dryer and is nearly completely recoveredwhereas the acetic acid is volatilized.

Objective criteria have been used for comparison of the protein staining(color development) ability of the aqueous liquid smoke composition ofthis invention with the tar-containing liquid smoke from which it isderived. These criteria include the "Staining Power" as applied to theliquid compositions themselves, and the "Staining Index" as applied tothe coating on the tubular food casing. In each instance, the testedembodiments of this invention demonstrated substantially the samestaining ability as the original tar-containing liquid smoke, yet thetar content has been reduced to a level such that the heretoforeexperienced tar problems had been eliminated. Staining index is areliable criterion for measuring the color development ability incasings of this invention which are freshly made, but as hereinafterdiscussed, Staining Index should not be used with aged casing. Theprocedure used for measuring staining power and staining index is asfollows:

Staining Power and Staining Index Procedure

This procedure has as its basis the reaction encountered in meatprocessing in which the meat protein reacts with the smoke components,thereby imparting a desirable dark smoked color to the product. Toquantify this staining or darkening power, the unknown smoke or freshlysmoke treated casing is reacted with a specific amino acid (glycine)under acidic conditions at 70° C. for thirty minutes. The absorbance ofthe solution is measured at 525 nm. This procedure can be run on liquidsmoke or liquid smoke treated casing with reproducible results. Thedetailed procedure is as follows:

I. Prepare a 2.5% solution of glycine in 95% acetic acid.

(a) Dissolve 12.5 g of glycine in 25 ml of water in a 500 ml volumetricflask. Add enough glacial acetic acid to facilitate the dissolution.

(b) Dilute to the prescribed level with glacial acetic acid.

II. In the case of liquid smoke analysis, weigh into a 15 ml test tubevial, 15-20 mg (±0.1 mg) of the liquid smoke to be evaluated, or

III. In the case of smoke treated casing analysis, punch out four doublethickness discs from the test casing to yield a total casing area of 2.0in² (12.9 cm) for the eight discs.

(a) If the casing is shirred, inflate a section with 10 psi 68,900Pascals air to smooth the surface. Collapse the casing by drawing itover a hard surface, punch out the discs and add them to the vial.

IV. To the vials containing either the liquid smoke or the treatedcasing, add 5.0 ml of the 2.5% glycine/acetic acid solution.

V. Cap the vials, hand shake to assure contact of the sample, and placein a 70° C. oven for thirty minutes.

VI. Measure the absorbance at 525 nm for each solution using the glycinereagent as a blank.

VII. The absorbance is reported as the staining power of the liquidsmoke or the staining index of the smoke treated casing.

The numerical value for staining index is the absorbance per 2 squareinches 12.9 cm² of casing surface.

The staining power represents the ability of a liquid smoke to develop acertain absorbance or color under the staining index procedure, i.e.,units absorbance per mg. liquid.

EXAMPLE III

A series of tests was performed in which as-is tar-containing liquidsmoke was partially neutralized from an initial pH of 2.3 to a final pHof 6.0 under controlled temperature conditions and also uncontrolledtemperature conditions. Staining power was determined at differentneutralization temperatures and the data is summarized in the FIG. 4graph for Royal Smoke AA liquid smoke (upper curve) and Charsol C-10liquid smoke (lower curve).

More particularly, the as-is liquid smoke used for each test waspartially neutralized by the addition of 50% NaOH with continuousmixing, and was cooled by means of an immersed coil-type portablerefrigeration unit to remove the heat of solution and maintain thetemperature of the liquid mixture at the desired level. After therequired amount of base was added to reach the desired pH of 6.0, thetar precipitate was separated by gravity and the tar-depletedsupernatant liquid was used for the staining power measurement.

Inspection of FIG. 4 reveals that the staining power of the partiallyneutralized Royal Smoke AA liquid smoke remains relatively constant atabout 0.027 in the controlled temperature range of 5°-30° C., whereasthe staining power of the partially neutralized Charsol C-10 liquidsmoke remains substantially constant at about 0.022 in the sametemperature range. At higher temperatures the staining power begins todiminish so that a temperature level of about 40° C. represents theupper limit for the method of this invention. For this particular seriesof tests and with uncontrolled temperature neutralization (no cooling),the maximum uncontrolled temperature reached by the liquid smoke mixturewas about 60° C.

EXAMPLE IV

A series of tests was performed which illustrates the importance of atleast partially neutralizing the as-is tar-containing liquid smoke(having an initial pH of about 2.3) to raise the pH to at least above 4and preferably no higher than about 8. In these tests several differenttypes of commercially available liquid smokes of different total acidcontents were at least partially neutralized by the controlled additionof 50% NaOH liquid, and the temperature of the mixture was controllablymaintained at about 15° C. during the mixing by employing an immersedcoil-type portable refrigeration unit. Samples were removed at variouspH values and their light transmittance was measured by adding 1 ml. ofthe liquid smoke to 10 ml. of water, mixing thoroughly and thenmeasuring transmittance at 715 nm with a spectrophotometer. Percentlight transmittance (relative to water) is inversely related to tarcontent of the tested liquid smoke, i.e., high tar content results in acloudy liquid with low light transmittance. As used herein, "lighttransmittance" of aqueous liquid smoke refers to the latter's intrinsiclight transmittance without addition of materials which maysignificantly affect the percent light transmittance.

The results of these light transmittance tests are plotted versus liquidsmoke pH in FIG. 5, and the curves for the four types of liquid smokeused in these tests are as follows: Royal Smoke AA (full line), RoyalSmoke B (dash line), Charsol C-12 (dash-dot-dash line), and Charsol C-10(dash-dot-dot-dash line). FIG. 5 illustrates that with differentwood-derived liquid smokes, the desired pH to achieve maximumtransmittance (and tar precipitation) varies somewhat, but generally isabove a pH of 4 and preferably is between a pH of 5 and 8. Above a pH ofabout 8 the tars tend to become resolubilized. However, since a lighttransmittance of at least 50% is considered to be the indicator showingthat the tar removal from the liquid smoke is sufficient to enable thetar-depleted liquid smoke to be used without the danger of tarprecipitation occurring during subsequent processing, it will beapparent that neutralization to a pH above 8 is suitable for several ofthe tested liquid smokes.

EXAMPLE V

Another series of tests was performed which demonstrates the differencebetween as-is tar-containing liquid smoke and the tar-depleted liquidsmoke of this invention, in terms of cellulose casing haze. Samples ofcasing with each type of liquid smoke incorporated therein were immersedin water. During this period, the incorporated smoke reacted with thewater. In the case of the tar-depleted samples, no incompatibility wasmeasured but with the tar-containing samples the tar precipitated withinthe casing wall, and water incompatibility in the form of a cloudy hazewas measured quantitatively.

Royal Smoke AA liquid smoke was used in these tests to treat the casingexternal surface with the as-is tar-containing liquid smoke and alsowith the tar-depleted liquid smoke in accordance with this invention.The latter was prepared by partial neutralization to a pH of 6.0 at10°-15° C. in the Example I manner. A special coating was first sprayedon the casing internal surface for improved peelability. In this andsucceeding Examples, the improved peelability solution was of the typedescribed in Chiu et al., U.S. Pat. No. 3,898,348. The delivery rate was3.0-5.0 mgs/sq.in. (0.46-0.77 mg/cm²) of casing surface and the range ofcompositions used in this solution is listed in Table C.

                  TABLE C                                                         ______________________________________                                        Improved Peelability Solutions                                                ______________________________________                                        Carboxymethyl Cellulose - sodium salt                                         (Hercules "CMC 7LF")                                                           0.8-1.0%                                                                     Water                                                                         40.0-45.0%                                                                    Propylene Glycol                                                              45.0-50.0%                                                                    Mineral Oil                                                                    5.0-10.0%                                                                    Polyoxyethylene sorbitan ester of higher                                      fatty acids ("Tween 80")                                                       0.5-1.25%                                                                    ______________________________________                                    

The tar-depleted liquid smokes were separated from the tar precipitateand incorporated in the casing external surfaces by the proceduredescribed in Example II. The liquid smoke was incorporated into eachcasing wall at a loading of about 10 mg/in² (1.55 g/cm²).

The 21 mm. diameter nonfibrous treated casings were shirred and 36 inch(91.4 cm) long samples were taken randomly from a deshirred stick,inflated with air to minimize shirring wrinkles, and immersed in 200 ml.of deionized water. Immersion time was at least one hour but not morethan three hours, i.e., only sufficient duration for complete moisturepenetration of the casing wall. After blotting the samples dry, casinghaze was measured using the general procedure outlined in ASTM Method D1003, Volume 35, "Haze and Luminous Transmittance of TransparentPlastics" (1977). The results of these tests are summarized in Table Das follows:

                  TABLE D                                                         ______________________________________                                        Casing Haze                                                                   Type Smoke                                                                    Haze        No. Determinations                                                                          Haze Range Ave.                                     ______________________________________                                        none        32            6.0-9.7%                                            (control)                                                                      7.9%                                                                         Tar-Depleted                                                                              32            5.9-8.5%                                             6.7%                                                                         Tar-Containing                                                                            32             8.5-13.1%                                          10.7%                                                                         ______________________________________                                    

It is apparent from Table D that the average haze for the as-istar-containing liquid smoke treated cellulose casing, is substantiallyhigher than the average haze for the tar-depleted liquid smoke treatedcellulose casing of this invention, such that the latter is only about53.4% of the former. Average haze values are also a function of casingdiameter and increase with increasing diameter because of the thickercasing wall. The absolute value for average haze further depends on thetotal acid content (or absorptive power as hereinafter discussed) of theparticular smoke and the amount of smoke incorporated in the casing but,in general, the average haze for the cellulose casings of this inventionis substantially lower than the average haze for cellulose casingstreated with as-is liquid smoke, even though their smoke color, odor andflavor developing capabilities for encased foodstuff products are aboutthe same when prepared under equivalent conditions. This relationshipdemonstrates the chemical and functional difference between thetar-depleted liquid smoke treated cellulose casings of this invention,and the as-is liquid smoke treated casing.

The haze test is only useful in characterizing the cellulose casings andnot the fibrous casings of this invention. This is because fibrouscasings are inherently opaque and have a very high average haze, e.g.,about 97.5% for untreated fibrous casings.

EXAMPLE VI

A series of ultraviolet absorption spectroscopy tests was performedusing tar-depleted liquid smoke treated cellulose food casing accordingto this invention and tar-containing as-is liquid smoke treated casing.These tests demonstrate the substantial difference between the two typesof casings. The tests involved three different types of wood-derivedliquid smokes: Charsol C-12, Royal Smoke AA and Royal Smoke B. In eachinstance the casing was a 21 mm. diameter cellulose casing having acoating of the previously described type on the internal surface forimproved peelability. In each instance the tar-depleted liquid smoke ofthis invention was prepared from the as-is mixture by partialneutralization at 10°-15° C. to a final pH of 6.0, using the Example Iprocedure. The tar-depleted liquid smoke and the tar-containing liquidsmoke were each applied to the casing exterior surface by the Example IIprocedure at a loading level of about 10 mg/in² (1.55 mg/cm²).

The ultraviolet absorption spectrum over the 350 to 210 nm. range wasrecorded for liquid samples obtained from various smoke treated casingsby way of the following procedure:

(a) A 100 in² (645 cm²) sample of liquid smoke treated casing wassubmerged in 200 ml of anhydrous methanol for a period of about 1 hourand then removed.

(b) Depending on the liquid smoke loading, further dilution must be madefor compatibility with the UV scanning equipment. In these instances theliquid smoke loading was about 10 mg/in² (1.55 mg/cm²) of casing and thesolution used for scanning comprised 4.96 ml. of methanol and 0.10 ml.of the extract from step (a).

(c) The UV spectrum was recorded in the 350 to 210 nm. range with thefollowing format: 2 second response/2 mm slit, 10 nm./cm. chart, 50nm/minute scan speed, and 0-200% transmittance scale. In order tomeasure the absorbance primarily due to tars present in the liquidsmoke, the spectrophotometer was zeroed using an extract solutioncontaining the lowest possible tar content. For any particular type ofliquid smoke, this was an extracted and neutralized (pH 5.0) smoketreated casing extract sample. Once zeroed in this manner, anyadditional absorbance in the UV spectrum was a quantitative measure ofthe tarry components present.

The results of these ultraviolet absorption tests are plotted in theFIG. 6 graph with the Charsol C-12 samples shown as solid lines, theRoyal Smoke AA samples as dash lines, and the Royal Smoke B samples asdash-dot-dash lines. Inspection of these curves reveals that thegreatest difference between the tar-depleted samples and thetar-containing samples occurs at about 210 nm. wave length althoughthere is a substantial difference over the entire scanned range of wavelengths. The difference is greatest with liquid smokes of highest totalacidity, highest absorptive power and highest tar content (Charsol C-12and Royal Smoke AA). The ultraviolet absorbance difference is less forRoyal Smoke B liquid smoke which has lower total acidity and lower tarcontent. The ultraviolet absorbance and percent light transmittancevalues at 210 nm. wave length are summarized in Table E, and show thatthe smoke extracts from the tar-depleted liquid smoke treated cellulosecasings of this invention have an ultraviolet absorbance at 210 nm. wavelength which is reduced by at least 52% compared to the smoke extractfrom the corresponding tar-containing as-is liquid smoke treated casinghaving the same total acid content and absorptive power.

                  TABLE E                                                         ______________________________________                                        Ultraviolet Comparisons at 210 nm Wave Length                                 for Smoke Extracts from Smoke Treated Casings                                 Perceived                                                                     Type of                                                                       Reduction in                                                                  Liquid Smoke                                                                  Absorbance  Transmittance Absorbance                                          ______________________________________                                        Charsol C-12                                                                  Tar-Depleted                                                                              80%           0.10      89%                                       Tar-Containing                                                                            14%           0.85      --                                        Royal Smoke AA                                                                Tar-Depleted                                                                              62%           0.21      83%                                       Tar-Containing                                                                             6%           1.22      --                                        Royal Smoke B                                                                 Tar-Depleted                                                                              27%           0.57      52%                                       Tar-Containing                                                                             6%           1.22      --                                        ______________________________________                                    

EXAMPLE VII

The external surfaces of 21 mm. diameter cellulose frankfurter casingswere treated with the tar-depleted liquid smoke composition prepared inthe manner of Example I using the Example II treatment procedure. Forpurposes of comparison, the same size casings untreated by liquid smokesolution were used with and without the aforedescribed enhancedpeelability solution spray-coated on the inner surface of these controlcasings. All casings were stuffed with either an emulsion of the beefmeat formulation of Table F or the high collagen meat formulation ofTable G.

                  TABLE F                                                         ______________________________________                                        Beef Formulation                                                              Ingredients         Weight (kg)                                               ______________________________________                                        Beef Chuck          22.68                                                     Beef Plate          22.68                                                     Salt                1.13                                                      Water               13.61                                                     Seasoning           0.45                                                      Sodium Nitrite (Prague Powder)                                                                    0.11                                                      ______________________________________                                    

                  TABLE G                                                         ______________________________________                                        High Collagen Formulation                                                     Ingredients         Weight (kg)                                               ______________________________________                                        Beef Chuck          9.98                                                      Beef Tripe          7.26                                                      Beef Shank          7.26                                                      Beef Cheek          7.26                                                      Regular Pork        13.61                                                     Water               9.98                                                      Salt                1.13                                                      Seasoning           0.45                                                      Sodium Nitrite (Prague Powder)                                                                    0.11                                                      ______________________________________                                    

The stuffed casings were processed under normal conditions oftemperature and humidity as commercially practiced, but without theconventional step of smoke treatment. Processing conditions weresufficient to cause the transfer of smoke color, odor and flavorconstituents from the casing to the frankfurters. The casings werepeeled from the finished meat on a High Speed Apollo Ranger PeelingMachine. Two processing chambers were used for the two types ofemulsions but they were programmed in the same manner to raise thetemperature from 140° to 180° F. over a one-half hour period with 10%relative humidity. The meat product was cooked to an internaltemperature of 155° F., (68° C.) and then cold water showered (47° F.,8° C.) for 10 minutes, followed by a ten minute chilled water shower(35° F., 1.6° C.). Promptly after this processing, colorimetric valueswere obtained using a Gardner XL-23 Colorimeter with a 1 cm apertureopening standardized with a white plate, all in accordance with standardoperating procedures described in the instruction manual for the GardnerXL-23 Tristimulus Colorimeter, which is commonly used in the industryfor the measurement of color and light intensity. Three locations oneach of ten frankfurters from each meat formulation were selected forreadings. Reading locations were approximately 1 inch (2.54 cm) fromeach frankfurter end and in the middle. Colorimetric "L" and "a" valueswere collected. The results of these peelability and colorimetric testsare summarized in Tables H and I.

                  TABLE H                                                         ______________________________________                                        Peelability Tests                                                             Sample                                                                        No. and    No.     No. Franks                                                                              No. Franks                                                                            Peelability                              Description                                                                              Franks  Peeled    UnPeeled                                                                              %                                        ______________________________________                                        H.sub.1 Untreated                                                                        104     19        85      18                                       control.sup.1                                                                 H.sub.2 Untreated                                                                        112     112       0       100                                      control with                                                                  enhanced peel-                                                                ability.sup.1                                                                 H.sub.3 Tar-depleted                                                                     256     253       3       99                                       with enchanced                                                                Peelability.sup.1                                                             H.sub.4 Untreated                                                                        96      12        84      13                                       control.sup.2                                                                 H.sub.5 Untreated                                                                        128     128       0       100                                      control with                                                                  enhanced peel-                                                                ability.sup.2                                                                 H.sub.6 Tar-depleted                                                                     128     120       8       94                                       sample with                                                                   enhanced peel-                                                                ability                                                                       ______________________________________                                         .sup.1 Beef formulation.                                                      .sup.2 High collagen meat formulation.                                   

                  TABLE I                                                         ______________________________________                                        Colorimetric Tests                                                            Colorimetric Values                                                                                   Std.                Std.                              Samples                                                                              L*       ΔL                                                                              Dev.   a**  Δa                                                                              Dev.                              ______________________________________                                        H.sub.2                                                                              46.46    --      0.77   16.23                                                                              --      0.39                              H.sub.3                                                                              44.51    -1.95   0.97   16.44                                                                              +0.21   0.46                              H.sub.5                                                                              51.88    --      0.87   13.04                                                                              --      0.37                              H.sub.6                                                                              48.94    -2.94   1.33   14.07                                                                              +1.03   0.63                              ______________________________________                                         *"L" values represent light vs. darkness: the lower the value, the more       dark the sample.                                                              **"a" values represent redness: the higher the value, the more red the        sample.                                                                  

Analysis of Table H indicates that peelability of the beef formulationsample based on this invention (sample H₃) was excellent with use of theenhanced peelability solution. Peelability of the high collagen meatformulation sample (Sample H₆) was good with use of the enhancedpeelability solution. Analysis of Table I indicates that the frankfurterproducts made in tar-depleted liquid smoke-treated samples showed adarker and more red color than the frankfurter products made in casingswhich were untreated by liquid smoke solution.

EXAMPLE VIII

Staining powers were measured for various compositions which were agedat elevated temperatures (relative to the neutralization temperatureduring preparation) for periods of up to 25 days. In a first series oftests, as-is Royal Smoke AA liquid smoke and tar-depleted liquid smokeneutralized to a pH of 6.0 at various temperatures in the 5°-30° C.range were used and aged at 100° F. (38° C.). In a second series oftests, as-is Charsol C-10 and tar-depleted liquid smoke neutralized atvarious temperatures in the same temperature range were used and alsoaged at 100° F. (38° C.) for periods of up to 25 days. In a third seriesof tests, as-is Royal Smoke AA liquid smoke and tar-depleted liquidsmoke neutralized at various temperatures in the 5°-30° C. range, wereaged at 70° C. for periods of up to 25 days. In a fourth series oftests, as-is Charsol C-10 and tar-depleted liquid smoke neutralized atvarious temperatures in the 5°-30° C. range were also used and aged at70° C. for periods of up to 22 days. The procedure for preparing thetar-depleted liquid smoke in these tests was the same as described inExample I, and the results of these tests are summarized in Table J.

Table J shows that the staining powers of as-is tar-containing liquidsmokes are substantially constant, i.e., unaffected by elevatedtemperature aging. In contrast, the staining powers of the tar-depletedliquid smokes of this invention continuously decline during elevatedtemperature aging at 70° F. 21° C. and 100° F. 38° C. over periods of upto at least 25 days. This decline is at an approximately constant andlinear rate, within the entire neutralization temperature range of5°-30° C. These tests demonstrate the chemical difference betweentar-containing liquid smokes and the tar-depleted liquid smokes of thisinvention.

                                      TABLE J                                     __________________________________________________________________________    Effect of Elevated Temperature Aging on Staining Power                                    Aging  Staining Power                                             Type of Smoke                                                                             Temperature                                                                          Original                                                                           5 days                                                                            10 days                                                                           15 days                                                                           20 days                                                                           25 days                               __________________________________________________________________________    As-is Royal Smoke AA                                                                      38° C.                                                                        0.032                                                                              0.032                                                                             0.032                                                                             0.032                                                                             0.032                                                                             0.032                                 Royal Smoke AA                                                                            38° C.                                                                        0.026                                                                              0.022                                                                             0.019                                                                             0.015                                                                             0.012                                                                             0.009                                 neutralized at                                                                5-30° C.*                                                              As-is Charsol C-10                                                                        38° C.                                                                        0.025                                                                              0.025                                                                             0.025                                                                             0.025                                                                             0.025                                                                             0.025                                 Charsol C-10                                                                              38° C.                                                                        0.020                                                                              0.018                                                                             0.016                                                                             0.013                                                                             0.011                                                                             0.008                                 neutralized at                                                                5-30° C.*                                                              As-is Royal Smoke AA                                                                      21° C.                                                                        0.034                                                                              0.033                                                                             0.034                                                                             0.034                                                                             0.030                                                                             0.034                                 Royal Smoke AA                                                                            21° C.                                                                        0.027                                                                              0.024                                                                             --  0.026                                                                             0.022                                                                             0.022                                 neutralized at                                                                5-30° C.*                                                              As-is Charsol C-10                                                                        21° C.                                                                        0.024                                                                              0.024                                                                             0.024                                                                             0.024                                                                             0.024                                                                             0.024                                 Charsol C-10                                                                              21° C.                                                                        0.022                                                                              0.021                                                                             0.020                                                                             0.018                                                                             0.017                                                                             --                                    neutralized at                                                                5-30° C.*                                                              __________________________________________________________________________     *Average values for neutralization temperatures of 5, 10, 15, 20 and          30° C.                                                            

EXAMPLE IX

A series of tests was conducted on smoke colored and smoke flavored foodproducts encased in cellulose casings. In these tests the externalsurfaces of 21 mm. diameter cellulose casings were treated with as-isRoyal Smoke AA liquid smoke and tar-depleted liquid smoke of thisinvention prepared by neutralization at 10°-15° C. to a pH of 6.0. Thetar-depleted liquid smoke was prepared by the same procedure describedin Example I, and the casings were treated with the liquid smokes by theprocedure described in Example II. The casings were stuffed with a highcollagen-content frankfurter meat emulsion and processed by theconventional steps of cooking, cold water showering and chilling. Thecolorimetric values were obtained with the same equipment used inExample VII and by the same procedure described in connection therewith.The results of these tests are summarized in Table K.

These tests indicate that even though the staining index of thetar-depleted smoke treated casings declined substantially during agingas compared with the as-is liquid smoke treated casings, the smoke colorof the stuffed food product in the low staining index casing wasunexpectedly quite satisfactory.

                                      TABLE K                                     __________________________________________________________________________    Effect of Elevated Temperature Aging on Color Developement Capability                          Casing                                                                             ΔL** of                                                                             Casing                                                                             ΔL** of                                           Fresh                                                                              Frankfurter                                                                          Type Aged Frankfurter                                        Loading                                                                            Staining                                                                           From Fresh                                                                           of   Staining                                                                           From Aged                              Type of Smoke                                                                             mg/cm.sup.2                                                                        Index                                                                              Casing Aging                                                                              Index                                                                              Casing                                 __________________________________________________________________________    As-in Royal Smoke AA                                                                      1.58 0.42 5.21   3 months                                                                           0.36 3.89                                                                at 40° C.                                 Royal Smoke AA                                                                            1.30 0.34 about  3 months                                                                           0.15 2.81                                   neutralized at        2***   at 40° C.                                 10-15° C.                                                              Royal Smoke AA                                                                            1.32 0.35 3.88   accel.*                                                                            0.18 2.38                                   neutralized at                                                                10-15° C.                                                              __________________________________________________________________________     *Accelerated aging at 50° C. for 72 hours.                             **L values are frankfurter colorimetric measurements and ΔL is the      difference (darker color) compared to a frankfurter sample not treated        with liquid smoke.                                                            ***Estimated.                                                            

EXAMPLE X

All of the previously described tubular food casing treatmentexperiments involved cellulose non-fibrous casings, but the invention isalso useful in treatment of cellulosic fibrous casings. In thisexperiment fibrous casing stock of about 6.3 inch flat width was treatedwith tar-depleted liquid smoke prepared from Royal Smoke AA as-is liquidsmoke solution by the procedure outlined in Example I.

After winding on a reeler-mechanism, the untreated cellulosic fibrouscasing was unwound and caused to move through a bath of the tar-depletedliquid smoke solution making only one dip, and immediately rewound onanother reel. This procedure allowed the excess solution to be absorbedfrom the casing exterior surface and penetrate the casing wall while onthe reel to provide the final treated casing. The dipping operation wasconducted in a manner such that the casing interior surface was not incontact with the tar-depleted liquid smoke solution. Dwell-time in thesolution was only a fraction of a second and the casing travel speedfrom reel-to-reel was about 350 feet/minute (107 m/min.). Thereel-applied casing tension was about 10 lbs (44.5 Newtons). Theestimated tar-depleted liquid smoke solution loading on the casing wasabout 24 mgs./sq. in. (3.7 mg/cm²) of casing surface. This particularmethod for manufacturing a liquid smoke-treated fibrous casing is notpart of the present invention but is claimed in copending applicationSer. No. 301,276 entitled "Liquid Smoke Impregnation of Fibrous FoodCasings" filed Sept. 11, 1981 in the name of H. S. Chiu.

The so-treated fibrous casing stock was then shirred in a manner wellknown to those skilled in the art, and separate casing samples were thenstuffed with ham and bologna and processed using conventional stuffingand processing methods, except that no smoke was applied in thesmokehouse. The ham and bologna products had acceptable color, odor andflavor due to the transfer of smoke color, odor and flavor constituentsfrom the smoke treated fibrous casing to the meat.

In a preferred embodiment of this invention, the tar-depleted liquidsmoke composition is prepared from tar-containing aqueous liquid woodsmoke solution having a total acid content (total acidity) of at leastabout 7 weight percent, and most preferably a total acid content of atleast about 9 weight percent. Total acid content is a qualitativemeasure of the tar content and Staining power (previously defined) ofas-is liquid wood smokes used by manufacturers. In general, higher totalacid content means higher tar content. The same is true of the totalsolids content of as-is liquid smoke. The procedure used by liquid woodsmoke manufacturers to determine total acid content and total solids areas follows:

Determination of Total Acid Content For Tar-Containing Liquid Smoke

1. Weigh accurately about 1 ml. of liquid smoke (filtered if necessary)in a 250 ml. beaker.

2. Dilute with about 100 ml. of distilled water and titrate withstandard 0.1 N NaOH to a pH of 8.15 (pH meter).

3. Calculate the total acid content as percent by weight of acetic acid,using the following conversion:

1 ml. 0.1000 N NaOH=6.0 mg. HAc

Determination of Total Solids

The procedure for determination of total solids in liquid smoke is asfollows:

1. Pipet about 0.5 ml. of liquid smoke on a tared 6 cm aluminum moisturedish fitted with a dried Whatman No. 40 filter paper disc, and weighaccurately. The liquid smoke should be clear, and filtration is used toinsure this condition.

2. Dry for two hours at 105° C. in a forced draft oven, or for 16 hoursat 105° C. in a conventional oven.

3. Cool to room temperature in a desiccator and weigh.

4. Calculate the total solids as percent by weight of the liquid smoke.

Table L lists the most commonly used and commercially availabletar-containing aqueous liquid wood smokes along with theirmanufacturer-reported total acid content (total acidity). Total solidscontent, staining power, and percent light transmittance at 590 nm. arealso reported for comparison. It will be noted from Table L that theas-purchased (as-is) wood smoke solutions with total acid content valuesless than about 7 weight percent have high light transmittance valuesgreater than 50% and low staining power. Their tar content is so lowthat their water compatibility is high. Accordingly, there is no need toremove tar from such wood smoke solutions in accordance with thisinvention. Also, their staining powers are so low that they are notcapable of performing the same smoke coloring and smoke flavoringfunction as the tar-depleted aqueous liquid smoke compositions of thisinvention. It should, however, be recognized that such low tar contentas-is liquid smoke solutions may be concentrated as, for example, byevaporation, and the so-concentrated liquid smoke solution then mayacquire the characteristics of a tar-containing liquid smoke which canbe advantageously treated in the manner of this invention. That is, suchconcentrated tar-containing liquid smoke acquires higher total acidity,total solids, and staining power.

                                      TABLE L                                     __________________________________________________________________________    Commercially Available Liquid Wood Smokes                                     Manufacturers                                                                             Total Acid.sup.e                                                                    Total Solid                                                                          % Light Staining                                                                           Absorptive                              Designation Content %                                                                           %      Transmittance                                                                         Power                                                                              Power.sup.d                             __________________________________________________________________________    Royal Smoke AA.sup.a                                                                      11.5-12.0                                                                           10.2   0       0.034                                                                              0.68                                    Royal Smoke A.sup.a                                                                       10.5-11.0                                                                           9.0    0       0.029                                                                              0.42                                    Royal Smoke B.sup.a                                                                       8.5-9.0                                                                             8.8    0       0.025                                                                              0.36                                    Royal Smoke 16.sup.a                                                                      10.0-10.5                                                                           17.6   0       0.026                                                                              0.62                                    Charsol C-12.sup.b                                                                        12.0-12.5                                                                           8.3    0       0.031                                                                              0.54                                    Charsol C-10.sup.b                                                                        11.5  not reported                                                                         0       0.028                                                                              0.40                                    Charsol X-11.sup.b                                                                        10.0  5.8    0       0.022                                                                              0.36                                    Charsol C-6.sup.b                                                                         6.7   4.8    73      0.016                                                                              0.22                                    Charsol C-3.sup.b                                                                         3.6   1.0    98      0.007                                                                              0.12                                    Smokaroma Code - 12.sup.c                                                                 12.0  10.5   0       0.034                                                                              --                                      Smokaroma Code-10.sup.c                                                                   10.2  5.1    0       0.027                                                                              --                                      Smokaroma Code-s.sup.c                                                                    8.0   2.4    26      0.017                                                                              --                                      Smokaroma Code-6.sup.c                                                                    6.2   1.9    75      0.014                                                                              --                                      __________________________________________________________________________     .sup.a Griffith Laboratories, Inc., 12200 South Central Avenue, Alsip, I1     .sup.b Red Arrow Products Co., P.O. Box 507, Manitowoc, WI.                   .sup.c Meat Industry Suppliers, Inc. 770 Frontage Road, Northfield, I1.       .sup.d Measured at 340 nm.                                                    .sup.e Also referred to as total acidity.                                

In another preferred embodiment of this invention, the tar-depletedaqueous liquid smoke composition has a total acid content of at leastabout 7 weight percent and most preferably a total acid content of atleast about 9 weight percent. The total acid content of the tar-depletedaqueous liquid smoke is a value of the acid equivalent, since theanalytical procedure for determining the total acid content of thetar-depleted aqueous liquid smoke provides a measure of the free acidplus the acid salts resulting from the partial neutralization. Totalacid content is a qualitative measure of the staining power (previouslydefined) of not only tar-containing liquid smokes but also tar-depletedliquid smokes prepared therefrom by the present inventive method. Asused herein, the total acid content of tar-depleted liquid smokecompositions is measured by a steam distillation recovery-titrationprocedure. This method is theoretically capable of quantifying the acidssuch as the acetate and formate, which are formed in the at leastpartially neutralized tar-depleted liquid smoke composition. From areaction standpoint, the acid present in the aqueous liquid smoke (infree or salt form) remains constant during the controlled temperatureneutralization. However, the recovery of these acids is only about 60%due to an inability to achieve complete azeotropic recovery withinreasonable distillation volumes. At present, a procedure providingquantitative recovery of all acidic compounds from the tar-depletedliquid smoke regardless of state is not readily available. Under thesecircumstances, the results obtained by the steam distillationrecovery-titration procedure are multiplied by a factor of 1.4 forconversion to the same total acid content basis used with tar-containingliquid smoke. Measurement of total acid, phenol and carbonyl contents insmoke treated casing is determined by the following procedures.

Determination of Total Acid Content for Tar-Depleted Liquid Smoke andCasings Treated Thereby

This determination is made from the milliequivalents of sodium hydroxide(NaOH) required to neutralize the milliequivalents of acetic acid (HAc)which are distilled upon acidification of the at least partiallyneutralized tar-depleted liquid smoke composition or treated casingsamples prepared from such compositions. "Milliequivalent" refers to theweight in grams of a substance contained in 1 ml. of a 1.0 normalsolution. The procedure is as follows:

1. Weigh accurately 5 gm. of tar-depleted smoke or measure 100 sq. in.of tar-depleted liquid smoke treated casing into a tared 800 ml.Kjeldahl flask.

2. Add boiling chips and 100 ml. of 2% (v/v) H₂ SO₄ to the flask, thereaction being 2NaAc+H₂ SO₄ →2HAc+Na₂ SO₄

3. Place a 500 ml. Erlenmeyer flask containing 100 ml. of deionizedwater into an ice bath, and use this water to collect the distillate.

4. Connect the sample-containing Kjeldahl flask to the steamdistillation apparatus.

5. Distill the sample until the distillate volume in the collectingErlenmeyer flask reaches 500 ml.

6. Titrate 100 ml. of distillate with 0.1 N NaOH to an end point pH of7.0, the reaction being HAc+NaOH→NaAc+H₂ O

7. Calculate the measured acid content as weight of acetic acid on thebasis that 1 ml. of 0.1 N NaOH is equal to 6.0 mg. of HAc, so measuredacid content in mg.=ml. of titrant×6.0.

8. Total acid content in mg.=1.4×measured acid content in mg.

9. For liquid smoke, express the value of total acid content in mg. asthe wt. % of the original liquid smoke sample. For casing, express thevalue of total acid content as mg. of acid per 100 square inches ofcasing surface.

The total acid contents of several tar-depleted liquid smokecompositions of this invention have been measured by this steamdistillation recovery-titration procedure, and are listed in Table M.For comparison, the same procedure has been used to measure the totalacid content of the as-is tar-containing liquid smokes from which thesecompositions were derived, and the results are also listed in Table M.It will be noted that the values are quite similar for the same type ofliquid smoke, whether it be tar-containing or tar-depleted. For example,as-is Royal Smoke AA liquid smoke has a total acid content of 11.1% andtar-depleted Royal Smoke AA liquid smoke has a total acid content of12.2%. For further comparison, as-is Royal Smoke AA liquid smoke, asmeasured by the dilution-titration procedure used by the manufacturerand outlined herein for tar-containing liquid smoke, has also beenincluded in Table M. This value of 11.4% is also very similar to thevalues for Royal Smoke AA based on the steam distillationrecovery-titration procedure.

                  TABLE M                                                         ______________________________________                                        Total Acid Content of As-Is and                                               Tar-Depleted Liquid Smoke                                                                Tar        Analytical Total Acid                                   Smoke Type Content    Method     Content in %                                 ______________________________________                                        Royal Smoke AA                                                                           as-is      Dilution/  11.4                                                               Titration                                               "          "          Steam      11.1                                                               Distillation/                                                                 Titration                                               Royal Smoke A         Steam      10.2                                                               Distillation/                                                                 Titration                                               Royal Smoke B         Steam      9.1                                                                Distillation/                                                                 Titration                                               Royal Smoke 16                                                                           "          Steam      9.8                                                                Distillation/                                                                 Titration                                               Charsol C-12                                                                             "          Steam      11.8                                                               Distillation/                                                                 Titration                                               Charsol X-11                                                                             "          Steam      10.5                                                               Distillation/                                                                 Titration                                               Charsol C-6                                                                              "          Steam      7.3                                                                Distillation/                                                                 Titration                                               Royal Smoke AA                                                                           Tar-Depleted                                                                             Steam      12.2                                                               Distillation/                                                                 Titration                                               Royal Smoke A                                                                            "          Steam      11.2                                                               Distillation/                                                                 Titration                                               Royal Smoke B                                                                            "          Steam      8.7                                                                Distillation/                                                                 Titration                                               Royal Smoke 16                                                                           "          Steam      11.2                                                               Distillation/                                                                 Titration                                               Charsol C-12                                                                             "          Steam      11.8                                                               Distillation/                                                                 Titration                                               Charsol X-11                                                                             "          Steam      11.2                                                               Distillation/                                                                 Titration                                               Charsol C-6                                                                              "          Steam      7.6                                                                Distillation/                                                                 Titration                                               ______________________________________                                    

Determination of Phenol and Carbonyl Content in Liquid Smoke-TreatedCasings

The samples are prepared by measuring and steam distilling 0.129 to0.194 m² (200 to 300 in²) of casing external surface, as described inthe procedure for determination of total acid content.

The reagents for the phenol determination are prepared with distilledwater, as follows:

1. Color solution--Dissolve 100 mg. ofN-2,6-trichloro-p-benzoquinoneimine in 25 ml. of ethanol, andrefrigerate. For the test, dilute 2 ml. to 30 ml. with water.

2. Buffer, pH 8.3--Dissolve 6.1845 gm. of boric acid in 250 ml. ofwater. Dissolve 7.45 gm. of potassium chloride in 250 ml of water.Dissolve 0.64 gm. of NaOH in 80 ml. of water. Mix the three solutionstogether.

3. 1.0% NaOH--Dissolve 1.0 gm. of NaOH in water. Dilute to 100 ml.

4. Standard solution--Dissolve 0.200 gm. of dimethoxyphenol (DMP) in2000 ml. water. Then dilute portions of this solution to providestandard solutions containing 1 ppm, 2 ppm, 4 ppm, 6 ppm, and 8 ppm ofDMP.

The procedure for phenol determination is a modified Gibbs method, asdescribed in Wild F, Estimation of Organic Compounds, 143, 90-94,University Press, Cambridge, 1953. In this procedure, the sequence is asfollows:

1st--In a 25 ml. flask, mix the four constituents in the order listed:

5 ml. bufer pH 8.3

5 ml. casing distillate, standard, or water (blank)

1 ml. 1% NaOH

1 ml. dilute color reagent

2nd--Shake, stopper and place in dark for 25 minutes.

3rd--Read absorbance at 580 nm.

4th--Prepare a standard curve using absorbance as the abscissa andstandard concentrations as the ordinate. Extrapolate concentration ofDMP in casing distillates from this curve.

5th--Calculate mg DMP/100 cm² casing using the following equation:##EQU3##

The reagents for the carbonyl determination are as follows:

1. Saturated solution of recrystallized 2,4-dinitrophenylhydrazine("DNP") in carbonyl-free methanol

2. Concentrated HCl

3. 10% Alcoholic KOH--Dissolve 10 gm. KOH in 20 ml. distilled water anddilute to 100 ml. with carbonyl-free methanol.

4. Standard solutions--Dilute 1 ml. 2-butanone (methyl-ethyl-ketone)(MEK) to 2000 ml. with distilled water. Then dilute portions of thissolution to provide standard solutions containing 0.8 ppm, 1.6 ppm, 2.4ppm, 4.0 ppm, and 8.0 ppm of MEK.

The procedure for carbonyl determination is a modified Lappan-Clarkmethod as described in the article "Colorimetric Method forDetermination of Traces of Carbonyl Compounds," Anal. Chem., 23, 541,542(1951). In this procedure, the sequence is as follows:

1st--In a 25 ml. flask, mix the three constituents in the order listed:

5 ml. of 2,4 DNP solution

5 ml. casing distillate, standard, or water (blank)

Note: casing distillate may require further dilution.

1 drop concentrated HCl

2nd--Digest the mixture for 30 minutes in 55° C. water bath.

3rd--After rapidly cooling the digested mixture to room temperature, add5 ml. 10% alcoholic KOH, shake and let stand for 30 minutes.

4th--Read absorbance at 480 nm.

5th--Prepare a standard curve using absorbance as the abscissa andstandard concentrations as the ordinate. Extrapolate concentration ofMEK in casing distillates from this curve.

6th--Calculate mg MEK/100 cm² casing using the following equation:##EQU4##

Absorptive Power

It will be recalled that both the staining power and staining indexmeasurement procedures involve chemical reaction, and apparently forthis reason the values measured at ambient temperature decline underelevated temperature aging conditions. As demonstrated in Example IX,this decline is not an accurate indication of the smoke color producedin stuffed food products using casings aged after treatment withtar-depleted liquid smoke.

Under these circumstances, additional measurement procedures notinvolving chemical reaction have been used in this invention todetermine the coloring capability of liquid smoke and the liquidsmoke-treated casing. This measurement procedure for liquid smoke istermed "absorptive power" and the measurement procedure for liquidsmoke-treated casing is termed "absorptive index".

In the procedure for measuring absorptive power, 10 mg. of liquid smoke(either tar-containing liquid smoke or tar-depleted liquid smoke) isplaced in a disposable vial and 5 ml. of methanol is added thereto. Thetwo components are mixed by inverting the vial, and the ultravioletabsorption value of the mixture is then measured at 340 nm. Thisparticular wave length is selected because spectroscopy measurementswith many liquid smokes indicate greatest linearity in this wave lengthregion. Absorptive power measurements for various as-is liquid smokesare included in Table L. A plot of these absorptive power measurementsas a function of total acid content or total solids content reveals anapproximately linear relationship.

It should be noted that whereas tar content is a significant contributorto the absorptive power measurement, I have discovered that tar onlycontributes to the staining of food in a minor way, if at all. Thus, incommercially available as-is smokes, absorptive power includes ameasurement of tar content and the color constituents such as carbonyls,phenols and acids. This means that absorptive power of as-is smokes andtar-depleted smokes may be used to rank them by smoke color ability.However, absorptive power of as-is liquid smoke cannot be numericallycompared with the absorptive power of tar-depleted smokes of thisinvention because of the absorptive effect of tars. Unlike stainingpower, the absorptive power of liquid smoke does not decline with aging.

EXAMPLE XI

A series of absorptive power measurements was performed on varioustar-depleted liquid smokes of this invention. In each instance the as-isliquid smoke was neutralized by the addition of NaOH flakes and theneutralization temperature was controllably maintained at 10°-15° C.These measurements are summarized in Table N.

                  TABLE N                                                         ______________________________________                                        Absorptive Power                                                              Type                                                                          of                                                                            Liquid Smoke     As-Is  Tar-Depleted                                          ______________________________________                                        Royal Smoke AA   0.51   0.40                                                  Royal Smoke A    0.45   0.36                                                  Royal Smoke B    0.35   0.33                                                  Charsol C-12     0.40   0.38                                                  Charsol C-6      0.22   0.22                                                  Charsol C-3      0.11   0.15                                                  ______________________________________                                    

Table N should be interpreted in light of the preceding discussionrelating to the effect of tar content on liquid smoke absorptive power.Inspection of Table N reveals that the absorptive power of atar-depleted liquid smoke of this invention is generally somewhat lowerthan the absorptive power of the tar-containing as-is liquid smoke fromwhich it is derived. This principle does not hold for Charsol C-6 andCharsol C-3 since these liquid smokes are very low in tar content tobegin with.

Table N also demonstrates that the tar-containing liquid smokes usefulin the practice of this invention have absorptive power values of atleast 0.25 and that there are tar-containing liquid smokes such asCharsol C-3 having absorptive powers in the as-is form which do notsatisfy this requirement. Table N further shows that the absorptivepower of the tar-depleted liquid smoke compositions of this inventionwill have values which are above 0.2, and preferably, the absorptivepower values will be about 0.3 or greater. It will also be recalled fromTable L that Charsol C-3 has a very high light transmittance of about98% because of its low total acid content and low total solids content,and controlled temperature neutralization does not significantly affectits light transmittance.

Absorptive Index

In the procedure for measuring absorptive index, 2 square inches 12.9cm² of liquid smoke-treated casing are cut out after drying, and placedin 10 ml. of methanol. After one hour of soaking time, the methanol hasextracted all of the smoke components out of the casing, and theultraviolet absorption value of the resulting smoke component-containingmethanol is determined at 340 nm. As with the absorptive powermeasurement, a 340 nm. wave length was selected because spectroscopymeasurements with many liquid smoke extracts from liquid smoke treatedcasings indicate greatest correlation with smoke loadings in thisregion.

EXAMPLE XII

A series of absorptive index measurements was made on casings usingthree different types of tar-depleted liquid smoke prepared inaccordance with this invention with neutralization to a pH of 6.0, andapplied at different loadings to the exterior surface of non-fibrousfrankfurter size gel stock casings in the Example II manner. The resultsof these experiments are summarized in FIG. 7, with Royal Smoke AAderived liquid smoke shown as a solid line, Charsol C-12-derived liquidsmoke shown as a dash line, and Royal Smoke B-derived liquid smoke shownas a dash-dot-dash line. This Figure permits the practitioner to firstselect the desired extent of smoke color in terms of absorptive index,and then determine the required loading of a particular tar-depletedliquid smoke onto the casing to achieve this smoke color. In FIG. 7 1mg/in² equals 0.155 mg/cm². The correlation between smoke color andabsorptive index is illustrated in the following Example XIII.

EXAMPLE XIII

A series of colorimetric tests was performed using frankfurters preparedin the manner of Example III in non-fibrous casings treated with variousliquid smokes including those on which Example XII is based. The resultsof these tests are summarized in Table O.

                  TABLE O                                                         ______________________________________                                        Casing Absorptive Index and                                                   Frankfurter Surface Light Intensity                                                                               Frankfurter                                                           Casing  Light                                     Type of    Sample  Loading  Absorptive                                                                            Intensity                                 Liquid Smoke                                                                             No.     Mg/cm.sup.2                                                                            Index   (-ΔL)                               ______________________________________                                        Royal Smoke AA                                                                           1       1.3      0.4     2.4                                       tar-depleted,                                                                            2       0.93     0.2     2.1                                       controlled 3       1.55     0.6     3.2                                       temperature                                                                              4       0.62     0.19    1.4                                       Royal Smoke AA,                                                                          5       1.75     0.5     3.4                                       as-is tar-                                                                    containing                                                                    Royal Smoke AA,                                                                          6       1.5      0.4     2.4                                       tar-depleted,                                                                 uncontrolled                                                                  temperature                                                                   ______________________________________                                    

In an attempt to quantify the desired light intensity changes needed toinsure adequate color development, Δ L values were determined and areincluded in Table O. In this instance, the meat emulsion was 50% beefchuck and 50% regular pork trim, and Δ L values were considered too lowif a 1.4 unit change in light intensity or less, occurred between Lvalues measured on frankfurters produced within a non-smoked controlcasing compared to a liquid smoke treated casing.

Table O shows that if the absorptive index is less than about 0.2, thesmoke loading is 4.0 mg./in² (0.62 mg/cm²) or less. This level of smokeloading does not generally give a desired reduction in light intensityto the meat product, i.e., color development is generally considered tobe insufficient. The medium reduction in light intensity for thefrankfurters processed in a casing with a liquid smoke loading of 8.5mg/in² (1.3 mg/cm²) is quite satisfactory for most end uses, so that thecorresponding absorptive index of at least 0.4 for the casing representsa preferred embodiment of the invention.

Table O also shows that embodiments of this invention have substantiallythe same staining ability as the original tar-containing liquid smoke.Comparison of Samples No. 3 and 5 shows that the tar content of theliquid smoke has very little influence on the staining ability of theliquid smoke. For practical purposes, the frankfurter light intensity of3.2 for casing Sample No. 3 is substantially equivalent to thefrankfurter light intensity of 3.4 for casing Sample No. 5.

Table O further shows that controlled temperature neutralization by thepractice of this invention is unexpectedly superior to uncontrolledtemperature neutralization since comparable frankfurter light intensitycan be achieved at a lower liquid smoke loading on the casing. This isseen by comparing Samples No. 1 and 6.

It should be noted that many factors associated with the food emulsionand processing conditions can affect background color and hence L and ΔL values. For example, meat derives much of its color from myoglobin.The color associated with the myoglobin content of meat is known to bedependent upon chemical reaction of myoglobin and the cure which, inturn, is affected by processing conditions such as temperature,humidity, time and air velocity. Accordingly, the Δ L values in Table Oare only relevant for these particular tests.

All of the previously described experiments relating to absorptive indexwere performed on non-fibrous cellulose casings of the same diameterpromptly after liquid smoke treatment and drying. Other tests have shownthat absorptive index is not significantly affected by variation incasing thickness. Still other tests have shown that absorptive indexvalues for fibrous casing treated with tar-depleted liquid smokeaccording to this invention are about the same as the absorptive indexvalues for non-fibrous cellulose casing with the same amount of smokeloading. By way of illustration, an absorptive index of about 0.5 wasobtained with a fiber-reinforced cellulosic casing of 115 mm. diametertreated with tar-depleted liquid smoke derived from Royal Smoke AA at aloading of 10.1 mg./in² (1.57 mg/cm²) of casing external surface. Theabsorptive index for a non-fibrous cellulose casing, treated with thesame amount of liquid smoke in the same manner, is found from othertests to be about 0.5.

EXAMPLE XIV

A series of tests was performed on tar-depleted frankfurter sizenon-fibrous cellulose casings to demonstrate the minor effect ofelevated temperature aging on absorptive index.

In these tests tar-containing as-is Royal Smoke AA liquid smoke wasneutralized to a pH of 5.0 by the addition of NaOH flakes with theneutralization temperature being controllably maintained at 10°-15° C.Absorptive index measurements were obtained from the tar-depleted liquidsmoke treated casing promptly after treatment and drying, and afterstorage periods of five and twelve weeks at ambient temperatures. Othersamples of the same casing were maintained at 100° F. (38° C.) andabsorptive index measurements were obtained at the same time intervals.These measurements are summarized in Table P.

                  TABLE P                                                         ______________________________________                                        Absorptive Index of Aged Casing                                               Time and Temperature                                                                           Absorptive Index                                             ______________________________________                                        Initial at 21° C.                                                                       --                                                           Five weeks at 21° C.                                                                    0.37                                                         Twelve weeks at 21° C.                                                                  0.37                                                         Five weeks at 38° C.                                                                    0.35                                                         Twelve weeks at 38° C.                                                                  0.36                                                         ______________________________________                                    

Table P demonstrates that aging has no significant effect on absorptiveindex. For this reason, the absorptive index requirements of thisinvention are to be understood as based on measurements at ambienttemperatures.

Although preferred embodiments of this invention have been described indetail, it is contemplated that modifications thereof may be made andsome features may be employed without others, all within the spirit andscope of the invention. For example, it should be understood that as-istar-containing liquid smokes which are advantageously treatable in themanner of this invention may be further concentrated by well-knowntechniques before or after treatment, and before use in accordance withthis invention. This may be desirable if the practitioner wishes toapply a highly concentrated form of tar-depleted liquid smoke to acasing wall.

Other contemplated variations from the as-described embodiments of theinvention include methods for separating the tar-containing liquid smokeinto a tar-enriched liquid fraction and a tar-depleted liquid smokefraction. In the Examples this was done by gravity decanting, but othermethods may be used as will be understood by those skilled in theliquid-liquid separation art. These methods include, for example, liquidcycloning and centrifugal separation.

The tar-depleted liquid smoke treatment of a tubular food casing surfacein the manner of this invention is preferably practiced under controlledenvironmental conditions wherein the presence of minute metal particlesis minimized. This is an important requirement since metal wearparticles (primarily iron, copper, brass) in contact with the casingreact with the liquid smoke coating, resulting in auto-oxidation,discoloration and even cellulose degradation of the treated casing. Thediscoloration and cellulose degradation occur only in the immediate areaof the metal contamination and seldom exceed 2-10 mm diameter in size.The cellulose degradation may sometimes be severe enough to cause casingbreakage during stuffing or processing. The materials of construction ofthe treatment apparatus is an important factor in minimizing minutemetal particles. These materials should be (1) of high wear resistance,and (2) nonreactive to the liquid smoke. It has been determined thatcertain metals and alloys are compatible with these stringentrequirements. They are: certain aluminum alloys, chrome plating, tinalloys, and certain stainless steels. Care must also be used in othersteps of casing manufacture and handling to minimize the presence ofminute metal particles.

EXAMPLE XV

Four samples of tar-depleted liquid smoke were prepared with varyinglight transmittance values using the controlled temperatureneutralization method. The as-is liquid smoke solution used was "CharsolC-12", and had an absorptive power of about 0.5 at a wave length of 340nm, and a pH of about 2. Each of the four samples were preparedessentially as in Example I except each was neutralized to a differentpH value to give a differing light transmittance value for each of theresulting tar-depleted liquid smoke solutions. The samples wereneutralized by the addition of flake NaOH and the temperature wasmaintained during the neutralization within a temperature between about10° C. to about 25° C. using refrigeration cooling coils. NaOH was usedin such an amount to neutralize the samples to achieve lighttransmittance values of about 20%, 50%, 60% and 80%. This was achievedby adding an amount of NaOH to give the final pH indicated in Table Q.After the desired amount of NaOH was added, the tar precipitates wereseparated from the supernatant liquid by filtration to give atar-depleted liquid smoke. The light transmittance was measured bydiluting 1 ml of tar-depleted liquid smoke with 10 ml of water, andmeasuring transmittance relative to water on a spectrophotometer at awave length of about 715 nm. A control sample was also made in the samemanner, except the as-is smoke was neutralized to a pH of about 6.0. InTable Q are shown the pH and the light transmittance of the tar-depletedliquid smoke product.

                  TABLE Q                                                         ______________________________________                                        Sample                 Light                                                  No.             pH     Trans.                                                 ______________________________________                                        1               4.69   20.8%                                                  2               4.60   50.2%                                                  3               4.70   61.3%                                                  4               4.95   84.3%                                                  Control         5.92   92.%                                                   ______________________________________                                    

The above prepared samples were applied to a gel stock nonfibrousfrankfurter casing (size No. 25) to give a loading of 15.5 grams persquare meter of liquid tar-depleted liquid smoke using the apparatus andmethod described in Example V. The casings were dried as in Example Vfor about 3 minutes at a drying temperature between about 80° C. toabout 120° C.

During the application of the tar-depleted liquid smoke, the casing wasobserved for tar spots thereon and the drying guides and the squeezerolls of the drying unit were observed for tar buildup. The results ofthe observations are summarized in Table R.

                  TABLE R                                                         ______________________________________                                                 Light                                                                Sample   Trans.    Observation                                                ______________________________________                                        1        20.8%     Tar deposits formed immediately                                               on casing. Heavy sticking on                                                  squeeze rolls. Tar deposits                                                   formed on drying guides.                                   2        50.2%     Tar deposits formed immediately                                               on casing. Slight sticking on                                                 squeeze rolls. Tar deposits                                                   formed on drying guides.                                   3        61.3%     Tar deposits formed immediately                                               on casing. No sticking on                                                     squeeze rolls. Tar deposits                                                   formed on drying guides.                                   4        84.3%     Tar deposits formed on casing                                                 after five minutes. No sticking                                               on squeeze rolls. Tar deposits                                                formed on drying guides.                                   Control  92%       No tar spots on casing. No tar                                                deposits on drying guides or                                                  squeeze rolls.                                             ______________________________________                                    

As can be seen from the above results, the problems due to the presenceof tar in the tar-depleted liquid smoke solution, as reflected by thelower light transmittance values, become less as the tar content islowered or the light transmittance value is increased. With tar-depletedliquid smoke with a light transmittance of about 20%, the difficultiescaused by the tars, in particular the sticking on the squeeze rolls,render the coating process inoperable and the composition is, therefore,unacceptable. As the light transmittance rises to about 50%, there arestill difficulties, such as slight sticking on the rolls andcommercially undesirable tar spots on the casing, but the application ofthe liquid smoke can still be carried out and a usable casing can stillbe made. At a light transmittance value of about 60%, a casing can beprepared that has few tar spots and is commercially more preferable,although spots are formed on the casing after extended periods ofoperation. At the higher light transmittance values of Sample 4 and thecontrol, a casing is formed that is commercially acceptable, there beingno tar spots thereon, and the coating process can be carried out on acontinuous basis without tar-buildup or sticking difficulties that wouldlead to shutting down of the process.

What is claimed is:
 1. A tar-depleted liquid smoke treated tubular foodcasing prepared by the steps of providing a tar-containing aqueousliquid smoke solution at temperature below about 40° C. and having anabsorptive power of at least about 0.25 at 340 nm. wave length; at leastpartially neutralizing said aqueous liquid smoke solution by contactinga high pH constituent therewith in sufficient quantity to raise the pHthereof to above about 4 to thereby form a tar-enriched fraction and atar-depleted liquid smoke fraction; controlling the temperature of saidaqueous liquid smoke solution during said neutralizing so that thesolution temperature does not rise above about 40° C.; separating saidtar-enriched fraction and said tar-depleted liquid smoke fraction torecover the latter as a tar-depleted liquid smoke; and treating asurface of a tubular food casing with said tar-depleted liquid smoke insufficient quantity to provide an absorptive index of at least about 0.2at 340 nm. wave length for the casing wall.
 2. A tar-depleted liquidsmoke treated casing according to claim 1 wherein only the outer wall ofsaid casing is treated with said tar-depleted liquid smoke such that theexterior surface of the so-treated casing is darker than the interiorsurface of said casing.
 3. A tar-depleted liquid smoke treated casingaccording to claim 1 wherein the initial staining index of said casingis at least 0.2.
 4. A tar-depleted liquid smoke treated casing accordingto claim 1 in which said high pH constituent raises the aqueous liquidsmoke solution pH to about
 6. 5. A tar-depleted liquid smoke treatedcasing according to claim 1 in which the solution temperature iscontrolled during the at least partial neutralization so as not to riseabove about 30° C.
 6. A tar-depleted liquid smoke treated casingaccording to claim 1 in which said high pH constituent raises theaqueous liquid smoke solution pH to about 6 and the solution temperatureis controlled during the partial neutralization so as not to rise aboveabout 30° C.
 7. A tar-depleted liquid smoke treated casing according toclaim 1 in which said casing comprises a non-fibrous cellulosic casing.8. A tar-depleted liquid smoke treated casing according to claim 1 inwhich said casing comprises a fibrous cellulosic casing.
 9. Atar-depleted liquid smoke treated casing according to claim 1 in whichsaid liquid smoke solution has a total acid content of at least about 7weight percent.
 10. A tar-depleted liquid smoke treated casing accordingto claim 1 in which said liquid smoke solution has a total acid contentof at least about 9 weight percent.
 11. A tar-depleted liquid smoketreated casing according to claim 1 in which said liquid smokecomposition has an absorptive power greater than about 0.2 at 340 nm.wave length.
 12. A tar-depleted liquid smoke treated casing according toclaim 1 in which the tar-depleted liquid smoke treatment provides anabsorptive index of at least about 0.4 at 340 nm. wave length for thecasing wall.